Optimal joint signal design and power control for CDMA with decision-feedback receivers subject to user QoS constraints

A synchronous code-division multiple-access (CDMA) channel is considered for which power control is available. Each of the users is assigned a quality-of-service (QoS) threshold that is measured in terms of a signal-to-interference ratio (SIR), and to cover the situation of multiple classes of users, these are allowed to be unequal to each other. The receiver is taken to be of the nonlinear decision-feedback type in which the users are successively detected. Given the processing gain of the system, which is no greater than the number of users, we minimize the required total power (i.e., the sum of the users' received powers) over all sets of signature sequences and power-control policies that allow the users to meet their required QoS constraints.